Term 2 Flashcards
Define aniseikonia
Aniseikonia is the terminology whereby there is a difference in the perceptual size and shape of images between both eyes
What are the 6 layers of an MAR coated lens
You’ve got hydrophobic layer that is water repellent, hard coat for anti scratch, anti reflective coating for the reduction of glare from artificial sources of light.. x2
Anisometropia
A difference in refractive error, between the two eyes, either one hypermetropic and other myopic, or on the contrary a large difference between the two refractive errors.
Asthenopia
Reduction in light transmission which MAR coatings avoid..
Name features of MAR coating
Hydrophobic, anti static, buffer, anti reflective, scratch resistant
Allows 99% of light through
Cosmesis element
Driving lens examples
Duravision by Zeiss
Drive X lens by Seiko
Reduces the oncoming glare from vehicles, increasing visual clarity and perception
RISKS OF UV EXPOSURE
Skin cancer, cataracts, retinal damage
Relationship between tints and UV
Not all tints contain UV blockers, yet they should contain UV coating
UV coating can be applied to certain lenses with no level of tints, however there is a correlation
What is a graduated tint
Graduated tints are generally darker at the top and lighter towards the bottom, offering a cosmesis sense of style
Describe photochromic lenses
These lenses react to UV light and through any exposure, darkens depending on temperature and light intensity - as modern cars have a UV windscreen filter, they not useful when driving turning dark
What direction of light do polarised lenses eliminate
They eliminate horizontal glared light - unpolarised light vibrates in many different directions potentially causing some discomfort, however polarised light travels and vibrates in one particular direction
Infrared radiation
Arise from industrial processes like furnaces and industries where heat is employed;
CR39 not useful material for IR absorbing filter ideally glass
IR filters often colour green due to ferrous oxide - pilots
Benefits of yellow, orange tints
Areas of low light contrast settings and blue light emissions
Eg - football, soccer, snow sports
Benefits of amber, rose tints
Enhancing colours and not suitable for driving conditions
Dark amber and brown tints
Melanin - decreasing blue light emissions, improving visual clarity and enhancing contrast
E.g - fishing, golf, cycling
Grey tints
doesn’t alter the perception of colours, natural perception and minimises brightness and glare
Any outdoor activity, reduces eye strain
Green tints
Soothing cool tones, enhances contrast, whilst preventing eye strain in bright conditions
Good, tennis baseball
Why bifocal recommendations
Clear vision for two distances
Wide and stable view
More convenient than two separate
Disadvantages
Less cosmesis
No intermediate
Limited view with small seg
What base prism does round seg innervate
Base down prism hence better to go for plus distance prescription
What base direction do D and C segs innervate
Base up prism hence suited to minus rx
Advantage of C over D seg
Offer bette cosmetics
Feature of executive Seg
Leat cosmesis as line running though lens
No jump henc offers best optics
Where should heights be taken from
Lower limbus
Define best form lens
Aimed to reduce or eliminate certain aberrations to allow clear vision focussing on retina, opposing distortions
What factors do longitudinal and transverse aberrations arise from
Dispersive properties of optical materials
Higher refractive index = lower v value hence higher dispersive
Pincushion distortion
Occurs in positive lenses whereby as you move away from optical centre the lens magnifies and extends
Advantages of aspheric lenses
Control of distortion
Less spec mag
Thinner and lighter lens hence better cosmesis
Considerably flatter
Off axis performance
